Printing method and product thereof



Patented Nov. 4, 1941 UNITED rmN'rrNG METHOD AND rno'nuc'r 'rmmnor Sylvia A. Nelson and mum r. Nelson,

- Ardmore, Pa.

No Drawing. Application March 1 4, 1939,

Serial No. 261,768

22 Claims.

I This invention relates to a printed paper and method of making the same and has particular reference to the production of printed glassine paper, though, as will be pointed out hereafter, the invention is more broadly applicable to the provision of printed paper of other types, such as vegetable parchment and .bond papers.

This applicationis in part a continuation of our application Serial No. 90,026, filed July 10, 1936.

The printing of glassine involves several 'difficulties due to both the extremely glossy supercalendered surface and the hydrated nature of the paper.

First, the highly supercalendered surface offers considerable resistance to penetration by ink vehicles and as a consequence special inks must be used for the printing process made up with vehicles capable of biting into the glossy surface. If some slight penetration does not occur, the ink will not adhere and offset may result, and the ink may be easily smeared on the product when it is handled in subsequent operations or in use. types containing suitable solvents or vehicles restrictsthem to certain pigments, whereas it would be desirable to be able to print glassine paper with any ink which could be used on ordinary papers which do not have such a highly calendered surface. The slight adherence of ink to a glassine surface prevents satisfactory embossing of printed glassine.

It is sometimes desired, in present-day printing, to use inks which may be quickly dried by the application of heat. The temperatures which must be used for the quick drying are such that, in general, substantial amounts of moisture will be removed from the paper which is subjected to the drying operation. In the case of glassine paper, this results in the removal of a substantial part of the moisture which contributes to the desirable qualities of glassine, namely, strength, transparency, and greaseproof properties. In fact, subjecting printed glassine to the temperatures which are used for ordinary heat drying will frequently bring the glassine almost to the point of charring and frequently blistering or charring will take place to some extent. Furthermore, the nature of. the glassine sheet from which moisture has been removed is such that the moisture cannot be reintroduced to bring it back to its original condition. In other words, any dehydration which occurs due to the heat drying finally determines the moisture content of the product.

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The fact that the inks must be of special A further objectionable feature of printing on glassine is that the printed matter is frequently substantially duller than the gldssy surface of the paper, giving an unattractive appearance to the product. As a consequence of this, resort has often been had to coating the printed glassine to secure the desired sheen over the entire surface, including the printing. A uniform gloss is much to be desired.

The various matters mentioned above are to a greater or less extent true of papers which are supercalendered to a degree less than glassine. Depending upon the degree cf supercalendering, such papers may be more or less resistant to the penetration and adhesion of ink vehicles, the printing thereon may be duller than the paper surface, and the properties may be injured by rapid heat drying after the supercalendering has takenplace.

In accordance with the present invention, the above objections are overcome by printing an uncalendered or preliminarily calendered paper prior to the supercalendering operation. Where heat drying is used, it also precedes the supercalendering.

The invention will be best understood by considering rather specifically the steps involved in securing a printed, coated, and embossed glassine.

Glassine is produced by the supercalendering of moistened greaseproof stock. The greaseproof paper is generally formed from a sulphite spruce pulp, though it may be formed from sulphate, sulphite, or other coniferous pulp, for example, of pine, hemlock, spruce or fir. The sheeted stock as it comes from the paper machine, is usually given a preliminary calendering treatment in running through the paper machine calenders. The product thus obtained has a relatively dull absorbent surface exhibiting none of the high gloss of the glassine paper which is to be ultimately produced. This paper is then moistened, rolled up, and left to season for a period of variable duration, depending upon the quality of the final product desired. Finally it is Y supercalendered' in the well-known fashion to ing to 212 F., and its surface is of such nature that it may be printed upon by practically any type of conventional ink. In accordance with the invention, the printing may be continuous with the flow of paper from the machine, though in general, since the speed of the printing might not be readily correlatable with the speed of formation of the paper, the paper will be taken from the machine, either with or without preliminary calendering, rolled up and later printed, either at the same or some other plant.

When heat drying is used, such drying will, of course, be effected immediately after the application of the printing to the paper. If the paper is printed immediately after coming from the paper machine driers, it will be warm and the ink drying will be facilitated. The heat drying of printed greaseproof paper of the type just indicated may reduce the moisture content to the range between none at all and five per cent., this moisture content meaning the amount that can be removed by" heating the paper to 212 F.; in other words, what might be considered as free moisture.

Unlike the case of glassine paper, however, moisture may be reintroduced into the printed greaseproof paper and to a controllable degree.

Following the heat drying, for example, it may be subjected to a water spray or water vapor and rolled up for the usual seasoning period. At this point a coating may be applied, in the form, for example, of a wax emulsion as more fully pointed out hereafter. It may then be supercalendered on the conventional glassine supercalendering apparatus and in the conventional fashion, the moisture content being regulated in the usual way by control of the amount of water added in the dampening and/or coating process, the temperature of the calendering rolls, and the speed of the supercalendering process. The final product thus obtained may have the usual glassine moisture content, say, six to nine per cent., despite the fact that the heat drying very much reduced the moisture content of the greaseproof paper. The moisture in the final product may, of course, be outside the range indicated, if desired. Following the supercalendering the glassine may be embossed in the usual way.

The product thus obtained involves none of the limitations in processing or drawbacks of the final products described above. Because greaseproof paper is printed, the ink does not have to be of special type. Heat drying may be used and any reduction of moisture content which accompanies the heat drying accepted without deleterious effect on the final product, since the moisture so removed maybe reinserted to a controlled degree to such extent that the final glassine will have the same moisture content and properties as conventional glassine. Furthermore, the printing is polished in the calendering operation, so that it has the same glossy appearance as the unprinted surface of the paper. This effect is particularly remarkable because it would not ordinarily be expected that the inked surface could be satisfactorily calendered without smearing or other injury, or that it would take on the same gloss. as the remainder of the surface. The appearance of the final product does not indicate that the printing is at all separate from the paper and, infact, is such that the printing appears to be an integral part of the paper and it might be suspected, on superficial examination, that the entire surface had been additional advantage to the supercalender-- ing of the printed surface is that the printing is caused to be an integral part of the paper to such extent that it is thoroughly protected against removal and will stand up under such subsequent processing as embossing.

The previse procedures to be followed in the practice of the present invention may be greatly varied. For example, an alternative method may involve the following:

Greaseproof paper may be formed'by sheeting the usual greaseproof stock, the sheet being then only partially dried and, if desired, treated with a'plasticizer of the type, for example, described in Bidwell Patents Nos. 1,914,798 and 1,914,799. The plasticizer comprising an aqueous solution, will, of course, raise the moisture content very considerably. Drying may then be resumed to bring the moisture content down to, say, 30%.

The greaseprof paper containing this amount of moisture is only slightly damp to the touch and may be printed upon in the same fashion as a dry paper. The amount of moisture thus provided at the time of printing may be accomplished, as pointed out above, if a plasticizer is added, or may be the result of direct drying without any plasticizing or other intermediate treatment. Immediately following the printing a suitable coating maybe applied in the form, for example, of an aqueous emulsion. Such an emulsion will, in general, have no effect whatever upon an ink which is made up with a nonaqueous vehicle. The printed and coated sheet may then be passed through a heat drying apparatus for the purpose of drying both the inkand the coating. Such heat drying apparatus, depending upon the period of drying and the temperatures used, may not only volatilize the ink vehicle and the water added with the coating, but may also reduce the moisture content of the paper to some extent. In general, however, satisfactory drying may be accomplished, attended by a reduction of moisture content which will still result in the maintenance of the moisture content after drying above 15 to 20%, so that the printed and coated paper will be in condition for immediate supercalendering. It will be noted that the moisture remaining is substantially that resulting from a drying operation and is consequently quite uniform so that there is no necessity for the addition of moisture after the printing operation. The resulting printed and coated glassine may be treated in any desired subsequent fashion, as, for example, by embossing.

In case the heat drying operation reduces the moisture content below that suitable for immediate supercalendering to form glassine, or in case it is desired to have the greaseproof paper somewhat drier prior to the printing operation, moisture may be added in the form of a spray or by exposing the paper to water vapor to bring its final moisture content up to the proper amount for the supercalendering operation. In any event, it is desirable to have as much moisture in the paper as practical at the end of the ink-drying operation, whether this be effected by heat or by exposure at ordinary temperatures, inasmuch as the moisture so remaining is uniformly distributed'and there is thereby minimized the necessity for allowing a substantial interval to elapse between the addition of other moisture, if that is required, andthe supercalendering operation.

It will be clear that in the last described procpaper.

ess coatings may be applied at any suitable stage in the procedure, either in the form of aqueous emulsions or in non-aqueous solutions.

As noted previously, the inks which may be used are practically any which may be used for printing ordinary paper stock. It is much cheaper to use common inks rather than those made up with special solvents which are designed for use upon supercalendered glassine or other supercalendered papers to which many ordinary inks are not readily applicable at all and to which the application of a great majority of inks of the socalled aniline types, for example, have been found to be very unsatisfactory without the taking of special precautions such as a reduction of moisture content of the supercalendered paper below the content most suitable for a satisfactory sheet. Another type of ink which may be used is that indicated several times previously adapted to be dried by the application of heat. Such inks are of the so-called vapor or heat-drying type, and involve liquid components which, by reaction and/or evaporation at temperatures from about 150 F. upwards, and generally above 212 F., leave solid products, and hence rapidly become dry. Such inks are generally rapidly dried at rather elevated temperatures, the drying becoming more rapidly effected as temperature is increased, and if glassine printed after its formation with such inks is subjected to the drying process, it may be injured, either merely by a lowering of its moisture content or by actual visible destruction by the formation of blisters. However, the process of using such inks on greaseproof paper and subjecting the printed greaseproof paper to heat dryi even though it may reduce the moisture content to practically zero, is not harmful, since the moisture may be reintroduced and supercalendering to glassine effected. As indicated above, the moisture content of the greaseproof paper may be caused to be extra high at the time of printing so that, despite reduction, there may still be sufficient for the direct production of glassine by supercalendering.

Examples of such heat-drying inks are given in the patents to Jeuck 2,042,432, dated May 26,

' 1936, and Gessler, 2,087,190, dated July 17, 1937.

As pointed out in those patents, ink vehicles may be used which at ordinary temperatures have only a low volatility, but are such that their vapor pressures increase very rapidly with increase of temperature, so that by subjection to elevated temperatures rapid setting of the ink will result, either by evaporation alone or by evaporation attended with combustion of the vapors. Where heat-drying inks are referred to herein, there are meant those inks which are intended to be subjected to elevated temperatures after printing to effect rapid drying, so that the use of slip sheets may be avoided. Inks of the heat drying type, as pointed out in the patents referred to above, are particularly adapted for rapid production work.

While specific inks have been mentioned, any ink will generally be satisfactory which does not provide an exceptionally heavy coatin on the Such inks will stand up under the abrasion incidental to supercalendering and will merely be polished by the supercalendering operation to the same extent as the surrounding unprinted portions of the paper, so that a uniform gloss over the whole surface will result, It is, of course, necessary to use an ink which will not be smeared r injuriously afiected by added moisture if moisture is added prior to the supercalendering operation. Such inks may be readily chosen from those which are 'well known and need not be described herein in detail.

In the examples described above, coating was eflected prior to supercalendering. Alternatively, the coating may be applied after the supercalendering operation, this being particularly desirable when the coating composition contains nonaqueous solvents. The supercalendering so protects and thoroughly dries the ink that coatings may be applied, if desired, which might not be applicable if the ink was applied without being followed by the supercalendering treatment or, at any rate, unless the printed sheet was exposed for some time prior to coating for complete evaporation or oxidation of the ink vehicle. In the present case, however, any suitable coating may be applied immediately after the supercalendering operation which follows 'the printing without affecting the printing, unless, of course, the solvent of the coating is of such nature as to attack the dried ink vehicle.

the supercalendering and after printing in the improved process, the application being in the form of an aqueous emulsion or a solution in a volatile solvent. The supercalendering in the presence of the wax gives a fine quality to the paper and further enhances the appearance of the printing. It will be obvious that coating, in general, may be associated with the process just described, the coating material, like the wax specifically referred to, being applied in the form of an aqueous emulsion or in a volatile solvent.

The printing of narrow webs of such papers as glassine frequently results in a tendency toward curling as the ink dries. In accordance with the present process, the full width of the paper machine web may be printed, then slit and subjected to the supercalendering operation or, if a narrow web is printed and then supercalendered, it is found that all tendency of the ink to curl the paper is avoided.

Heretofore, where embossed glassine was being made, it was customary to precede the printing by embossing. In fact, this was practically necessary, since the embossing might injure a preprinted web. In connection with the present invention, however, since the ink is protected by the supercalendering operation, it is found that the paper may be thereafter embossed without afiecting the ink. Furthermore, there is avoided the uneven printing resulting from an attempt to apply an ink to an embossed paper, the unevenness of which would frequently cause the ink to fail to provide the proper result; for example, fine lettering might become illegible. In the present case, even fine lettering will be perfect and unaffected by the embossing.

The invention has been particularly described with reference to glassine, which raises special problems in connection with printing but it will be obvious that it is of broader application to the printing prior to supercalendering of other papers. This is true, for example, where curl is to be reduced or where, in the supercalendering process, moisture may be introduced which would be removed upon heat drying, or where a supercalendered paper might be injured by the heat drying and a paper which is not supercalendered might not, even though some moisture was removed in the drying process. Furthermore, as in the case of glassine paper, many inks cannot be used with supercalendered papers which may be used on uncalendered or moderately calendered papers. In any such case where a supercalendered surface is not adapted to be printed satisfactorily with an ink, the printing may be accomplished prior to the formation of such surface, and the supercalendering then performed. The results in the way of appearance obtained by supercalendering after printing will, in general, be found to be similar to those produced in connection with glassine; namely, the entire surface of the paper, including the parts to which ink is applied, will have a relatively uniform gloss.

The advantages of the invention herein described, with particular reference to glassine, result to a noteworthy extent from the-application of the various features of the invention to two other papers, which may be particularly noted, namely, bond paper and vegetable parchment.

Bond paper when subjected to supercalendering in a state in which it contains substantial moisture, is not rendered transparent to the same degree as glassine, but its transparency is very considerably increased. The primary result of supercalendering of bond paper is the production of an extremely glossy, closed and hard surface which is adapted for many purposes, and particularly the production of high-grade printed matter. The surface thus produced by supercalendering is hydrated and, just as in the case of glassine, impenetrable to a satisfactory extent by many inks. It is also liable to damage by elevated temperatures such as those involved in the use of heat-drying inks, and moisture removed by such heat cannot be reintroduced into the supercalendered paper to raise its moisture content 'to a satisfactory point to achieve desired maximum strength and flexibility. Accordingly, the various practices in accordance with the invention, described specifically as applied to glassine, may be applied to bond paper, which, in a state prior to supercalendering, when it is either not calendered at all or calendered only to the extent of machine calendering, may be printed with the use of heat-drying inks or other inks which might not satisfactorily print the supercalendered bond, and is then subjected to the supercalendering operation as described in connection with glassine. After the supercalendering it may be embossed or coated, or the coating may be efiected prior to the supercalendering. In general, all of the steps herein described as applicable to glassine may be applied thereto and the specific treatment of bond paper need not, therefore, be separately described.

The invention is also applicable to vegetable parchment in the same fashion as to glassine and bond paper. Vegetable parchment is produced by treating a suitable stock with strong sulphuric acid producing a strong paper highly resistant to deterioration by water and showing a high degree of impenetrability to grease. Such paper in its original state is not particularly transparent, but when treated with moisture before or during the super alender operation, it acquires a very hard, glossy hydrated surface, and its transparency is very considerably increased corresponding to some extent to the increase of transparency resulting when greaseproof paper is supercalendered to form glassine. The problems involved in printing with or without heating involved in connection with glassine are also involved in connection with supercalendered vegetable parchment, the surface of which is particularly susceptible to damage by the elevated temperatures involved in printing with heat drying ink. Vegetable parchment is also much more readily printed by most inks before supercalenderlng than after supercalendering.

All the steps applicable to glassine as described herein are equally applicable to vegetable parchment, and hence they need not be repeated specifically for the treatment of vegetable parchment. It may be remarked that embossing following printing and supercalendering of vegetable parchment is a particularly noteworthy practice, since an attempt to emboss supercalendered vegetable parchment which has been printed after supercalendering is generally unsatisfactory because of the relatively slight adhesion of the ink to the hydrated supercalendered surface.

It may be remarked that in connection with the supercalendering of vegetable parchment, bond papers and book papers, water is generally introduced by steam or vapor jets to the paper during its passage through the supercalender rolls, because supercalendering of these papers does not generally require as much addition of water as the supercalendering of greaseproof to form glassine. Vegetable parchment, however, is sometimes dampened in the same fashion as that conventionally used for the treatment of greaseproof prior to its supercalendering to form glassine. In all cases, however, very substantial hydration occurs with the production of an impervious, hard, and glossy surface readily destroyed by heat and with substantial increase in transparency.

In certain applications of the process, loading may be required in the heaters or on the paper machine in cases where supercalendering would otherwise give too much transparency to the paper, for example, in the case of bond to be used for writing paper. A dense white paper having a glossy appearance may be produced, for example, by loading greaseproof stock with titanium dioxide and then supercalendering. By printing prior to supercalendering a product results which has a fine, even, glossy appearance.

Coating or laminating may be carried out in the usual fashion. It may be noted that the process is also applicable to the printing of a laminated sheet as well as the printing of plain sheets. For example, sheets of greaseproof may be laminated by waxy or resinous materials and may then be printed. Thereafter the laminated sheet may be supercalendered to produce, in effect, a laminated glassine sheet.

The products of the improved method are novel and readily recognizable. In the case of glassine or similar paper, the ink is burnished to the same degree as the remaining portions of the paper and, as noted above, appears to be a substantially integral part of the paper structure rather than the result of a printing operation. In the case of an embossed product, the ink is uniformly distributed over the entire surface and is not merely localized or more concentrated upon the high spots of the embossed paper.

It will be understood that by supercalendering there is' referred to herein that type of treatment which is exemplified by the formation of glassine from greaseproof paper, though commonly used for the attainment of similar results with other papers. That is, there is referred to capable of absorbing," and therefore adapted to the treatment involving passing a moist web the production of a relatively hard and closed.

surface, quite impervious to most liquids which are not water-soluble. The rollers used in supercalendering usually comprise pairs of polished metal rollers or composition and fabric rollers,

though the make-ups of superalender stacks may vary quite considerably. supercalendering results in a substantial increase of transparency of a paper which does not contain opaque flller. supercalendering is. thus contrasted with machine and other ordinary calendering, which in general does not greatly reduce the absorptive properties of a paper nor produce a high grade of polish nor affect to a substantial degree its transparency. Generally, furthermore, ordinary calendering as distinguished from supercalendering, does not produce a surfac which is destructively influenced by temperatures of the order of 212 F., and if an ordinary calender paper loses moisture by subjection to any such temperature, the moisture may be reintroduced into the paper to restore practically those conditions which existed prior to its removal.

It will be understood from the above that though the invention is particularly applicable to the production of printed glassine paper, and papers'as above described having similar inkrepellant or heat-sensitive properties, it is by no means limited thereto, since certain advantages may be secured by its application to the printing of other papers such as book papers.

What we claim and desire to protect by Letters Patent is:

1. The method of producing a printed paper having asmooth supercalendered surface not sufficiently absorptive of, and consequently not adapted to be printed with, a particular ink, comprising printing an exterior surface of the paper with said ink prior to formation of said supercalendered surface and while it has a surface capable of absorbing, and therefore adapted to be printed by, the ink, and then supercalendering the paper to modify said printed exterior surface of the paper and produce said insufliciently absorptive, smooth surface.

2. The method of producing a printed paper having a smooth supercalendered surface: liable to be damaged by heat and therefore not adapted to be printed with a particular heat-drying ink, comprising printing an exterior surface of the paper with said ink prior to formation of said supercalendered surface and while it has a surface not liable to damage by ink-drying heat and therefore adapted to be printed by the ink, exposing the printed paper to heat to dry the ink, and then supercalendering the paper to modify said printed exterior surface of the paper to produce said smooth surface.

3. The method of producing an inked paper receive, the ink, and while it has a surface not.

liable to damage by ink-drying heat, exposing the paper toheat to dry the ink, and then supercalendaring the paper to modify said printed exterior surface of the paper to produce said smooth surface.

4. The method of producing a printed paper having a smooth coated supercalendered surface not sufficiently absorptive of, and consequently not adapted to be printed with, a particular ink, comprising printing an exterior surface of the paper with said ink prior to formation of said supercalendered surface and while it has a' surface capable of absorbing, and therefore adapted to be printed by, the ink, and then coating said surface and supercalendering the paper to modify said printed exterior surface of the paper and produce said insufliciently absorptive, smooth surface.

5. The method of producing a printed paper having a smooth coated supercalendered surface liable to be damaged by heat and therefore not adapted to be printed with a particular heatdrying ink, comprising printing an exterior surface of the paper with said ink prior to formation of said supercalendered surface and while it has a surface not liable to damage by ink-drying heat. and therefore adapted to be printed by the ink, exposing the printed paper to heat to dry the ink, and then coating said surface and supercalendering the paper to modify said printed exterior surface of the paper to produce said smooth surface.

6. The method of producing a printed paper having a smooth coated supercalendered surface liable to be damaged by heat and therefore not I adapted to be printed with a particular heatdrying ink, comprising printing an exterior surface of the paper with said ink prior to formation of said supercalendered surface and while it has a surface not liable to damage by ink-drying heat and therefore adapted to be printed by the ink, applying a coating to the printed surface, exposing the printed paper to heat to dry the ink, and then supercalendering the paper to modify said printed exterior surface of the paper to produce said smooth surface.

7. The method of producing printed glassine comprising printing, prior to supercalendering,

the surface of paper formed from hydrated greaseproof stock, and then supercalendering said printed paper while moist to produce glassine.

8. The method of producing printed glassine comprising printing with a heat-drying ink, prior to supercalendering, the surface of paper formed from hydrated greaseproof stock, exposingthe printed paper to heat to dry the ink, increasing the moisture content of the paper, and then supercalendering the paper while moist to produce glassine.

9. The method of producing coated printed glassine comprising printing, prior to supercalendering, the surface of paper formed from hydrated greaseproof stock, and then coating and supercalendering said printed paper while moist to produce glassine.

10. The method of producing embossed printed glassine comprising printing, prior to supercalendering, the surface of paper formed from hydrated greaseproof stock, supercalendering-said printed paper while moist, and embossing the resulting glassine.

11. Printed glassine having both printed and unprinted portions of the surface in burnished content of the sheet, and then supercalendering the printed sheet.

15. The method of producing coated printed supercalendered bond paper, comprising printing, prior to supercalendering, the surface of bond paper, and then coating and supercalendering said printed bond paper.

16. The method of producing embossed printed supercalendered bond paper comprising printing, prior to supercalendering, the surface of bond paper, supercalendering said printed bond paper, and embossing the resulting supercalendered sheet.

.17. Printed bond paper having both printed and unprinted portions of the surface in burnished condition characteristic of supercalendering after printing.

men-r31 18. The method of producing printed supercaiendered vegetable parchment comprising printing, prior to supercalendering, the surface of vegetable parchment, and then super-calendering said printed vegetable parchment.

19. The method of producing printed supercalendered vegetable parchment comprising printing with a heat-drying ink, prior to supercalendering, the surface of vegetable parchment, exposing the printed sheet to heat to dry the ink, increasing the moisture content of the sheet. and then supercalendering the printed sheet.

20. The method of producing coated printed supercalendered vegetable parchment comprising printing, prior to supercalendering, the surface of vegetable parchment, and then coating and supercalendering said printed vegetable parchment.

21. The method of producing embossed prin supercalendered vegetable parchment comprising printing, prior to supercalendering, the surface of vegetable parchment, supercalendering said printed vegetable parchment, and embossing the resulting supercalendered sheet.

22. Printed vegetable parchment having both printed and unprinted portions of the surface in burnished condition characteristic of supercalendering after printing.

SYLVIA A. NELSON. ROBERT F. NELSON. 

